The U.S. Department of Homeland Security says it has issued an updated terrorism threat advisory taking into account this week's mass shooting in Orlando, Florida.

Homeland Security Secretary Jeh Johnson said Wednesday that security officials are particularly concerned about "homegrown violent extremists who could strike with little or no notice," especially since the Orlando attacks.

"Increased public vigilance and awareness continue to be of utmost importance," the updated advisory said.

Recent attacks in San Bernardino, California; Paris; Brussels; and now Orlando indicate that terrorists "will consider a diverse and wide selection of targets for attacks," the Homeland Security notice said. It was labeled a "bulletin," the lowest of three levels of alert messages.

Terrorists' use of the internet as a recruiting tool "to inspire individuals to violence or join their ranks" remains a major concern, the advisory said.

The Department of Homeland Security also is concerned about threats and violence targeting particular communities and individuals, "based on perceived religion, ethnicity, nationality or sexual orientation."

The advisory was released just a day before a previous version issued in December was set to expire. It remains in effect until mid-November, when Homeland Security is expected to issue a new assessment ahead of the U.S. holiday season.